Carbon compounds as fuels and feedstock

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Crude Oil and Hydrocarbons

Crude oil is a finite resource found in the Earth's crust; it is a thick, sticky, black liquid found in porous rock under the ground and under the sea.
It formed over millions of years from the effects of high pressures and temperatures on the remains of ancient biomass, mainly plankton, that was buried in mud.
Crude oil is a complex mixture of many different hydrocarbon compounds of different sizes.
A hydrocarbon is a compound that contains hydrogen and carbon atoms only.
The hydrocarbon molecules in crude oil have a carbon backbone that can be a chain or a ring, with hydrogen atoms attached.
Crude oil is being used up much faster than it is formed, so it is a finite resource.
Crude oil is the main source of fuels such as petrol and diesel, and also provides feedstock (raw materials) for the petrochemical industry.

Alkanes and Homologous Series

Alkanes are a homologous series of saturated hydrocarbons, meaning they contain only single carbon-carbon bonds.
The general formula for alkanes is CnH2n+2.
The first four alkanes are methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10).
A homologous series is a family of organic compounds that have the same functional group, the same general formula, similar chemical properties, and a gradual change in physical properties.
Each member of a homologous series differs from the next by a -CH2- unit.
Alkanes are generally unreactive, but they undergo combustion, can be cracked into smaller molecules, and react with halogens in the presence of light.
Methane is the major component of natural gas.

Fractional Distillation of Crude Oil

Crude oil is separated into fractions by fractional distillation; each fraction contains hydrocarbons with a similar number of carbon atoms.
The process works because different hydrocarbons have different boiling points, which depend on the size of the molecule.
Fractional distillation takes place in a fractionating column with a temperature gradient: it is very hot at the bottom and cooler at the top.
The crude oil is heated and vaporised; vapours rise up the column.
Hydrocarbons with high boiling points condense at the bottom of the column, while those with lower boiling points rise and condense at the top.
The fractions are tapped off as liquids at different heights according to their boiling points.
Smaller hydrocarbon molecules are collected at the top as gases; larger hydrocarbon molecules are collected lower down.
Fractional distillation is a physical process, not a chemical change.

Fractional distillation apparatus

Uses of Crude Oil Fractions

Liquefied petroleum gas (LPG) is used for domestic heating and cooking.
Petrol (gasoline) is used as fuel for cars.
Kerosene is used as jet fuel.
Diesel oil is used as fuel in diesel engines.
Heavy fuel oil is used for ships and power stations.
Bitumen is used for making roads.
The petrochemical industry uses crude oil fractions to produce polymers, lubricants, solvents, detergents and adhesives.

Properties of Hydrocarbons

As the size of hydrocarbon molecules increases, their boiling point increases.
This is because larger molecules have greater intermolecular forces of attraction, so more energy is needed to separate them.
Viscosity is the ease of flow of a liquid; high viscosity means thick and flows less easily.
Viscosity increases as hydrocarbon chain length increases, due to stronger intermolecular forces.
Flammability (ease of ignition) decreases as hydrocarbon molecules get larger; smaller molecules are more flammable and easier to ignite.
These properties influence how hydrocarbons are used as fuels: smaller molecules are useful as fuels, while larger, more viscous alkanes are useful as lubricants.

Combustion of Fuels

A fuel is a substance that releases energy in an exothermic reaction when burned.
Complete combustion occurs with an excess supply of oxygen and produces carbon dioxide and water.
During combustion, the carbon and hydrogen in the fuel are oxidised (gain oxygen).
Example: propane undergoes complete combustion: C3H8 + 5O2 → 3CO2 + 4H2O.
Incomplete combustion occurs with an insufficient supply of oxygen and produces carbon monoxide, carbon (soot) and water.
Carbon monoxide is a toxic, odourless gas that binds to haemoglobin, preventing it from carrying oxygen; it can cause dizziness, loss of consciousness and death.
Carbon dioxide is a major contributor to global warming; incomplete combustion also produces unburnt hydrocarbons and carbon particulates.

Acid Rain: Nitrogen Oxides and Sulfur Dioxide

Fossil fuels often contain sulfur impurities; when burned, the sulfur is oxidised to sulfur dioxide (SO2).
Sulfur dioxide dissolves in rainwater to form sulfuric acid, which contributes to acid rain.
Nitrogen oxides (NO and NO2) are formed when nitrogen and oxygen from the air react in the high temperature and pressure conditions of internal combustion engines.
Nitrogen dioxide reacts with rainwater to form nitrous and nitric acids, which also contribute to acid rain.
Acid rain causes corrosion of metal structures and buildings, damages carbonate rocks (e.g., statues), harms aquatic organisms, pollutes crops and water supplies, and irritates lungs, throats and eyes.
Catalytic converters in vehicles contain transition metal catalysts (platinum, palladium, rhodium) in a honeycomb structure to increase surface area.
In a catalytic converter, carbon monoxide is oxidised to carbon dioxide, nitrogen oxides are reduced to nitrogen gas, and unburned hydrocarbons are oxidised to carbon dioxide and water.

Hydrogen as a Fuel

Hydrogen reacts with oxygen in an exothermic reaction: 2H2 + O2 → 2H2O.
Advantage: hydrogen releases more energy per kilogram than any other fuel (except nuclear fuels).
Advantage: hydrogen does not pollute when burned because it only produces water.
Disadvantage: hydrogen is expensive to produce and requires energy for the production process.
Disadvantage: hydrogen is difficult and dangerous to store and move around; it is usually stored as liquid hydrogen in highly pressurised containers.
Disadvantage: the production of hydrogen releases carbon dioxide.
Most of the world's energy supply still comes from fossil fuels (over 80%).

Diagram showing the movement of hydrogen, oxygen and electrons in a hydrogen-oxygen fuel cell

Cracking and Alkenes

Cracking is an industrial process that breaks long-chain hydrocarbon molecules into smaller, more useful molecules.
It is used because the demand for short-chain fractions (such as petrol, kerosene and diesel) is greater than the supply, while there is a surplus of long-chain fractions (such as fuel oil).
Catalytic cracking involves heating hydrocarbons to about 470–550°C to vaporise them, then passing the vapours over a hot powdered aluminium oxide catalyst.
Steam (thermal) cracking uses higher temperatures and mixes the vaporised hydrocarbons with steam.
Cracking produces a mixture of shorter alkanes and alkenes; hydrogen and a higher proportion of alkenes are formed at higher temperatures and pressures.
Alkanes are saturated (single C–C bonds); alkenes are unsaturated (contain a C=C double bond) and have the general formula CnH2n.
Alkenes are more reactive than alkanes and are used to make polymers and as starting materials for many chemicals.
Test for alkenes: bromine water (orange) is decolourised by alkenes; it remains orange with alkanes.
In a cracking equation, the total number of carbon and hydrogen atoms must be the same on both sides (Law of Conservation of Mass).

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1.Which of the following is the general formula of the alkenes?
Easy
- ACnH2n
- BCnH2n+2
- CCnH2n-2
- DCnH2n+1OH
2.Which of the following is the molecular formula of propane?
Medium
- AC3H8
- BC3H6
- CC3H4
- DC3H10
3.Which of the following is the molecular formula of ethene?
Medium
- AC2H4
- BC2H6
- CC2H2
- DC2H8
4.Which of the following is the correct definition of a hydrocarbon?
Easy
- AA compound that contains carbon and hydrogen atoms only
- BA compound that contains carbon, hydrogen and oxygen atoms
- CA mixture of carbon and hydrogen gases
- DA compound that contains carbon and hydrogen atoms, and may contain other elements
5.Crude oil is a mixture of hydrocarbons.
Easy
True or false?
6.Fractional distillation separates crude oil into fractions by chemical reactions.
Medium
True or false?
7.Which fraction of crude oil is used as jet fuel?
Medium
- AKerosene
- BPetrol
- CDiesel oil
- DBitumen
8.Which fraction of crude oil is used for making roads?
Medium
- ABitumen
- BKerosene
- CDiesel oil
- DLiquefied petroleum gas

Soal lainnya

9.Which of the following properties increases as the chain length of a hydrocarbon increases?
Medium
- ABoiling point
- BFlammability
- CVolatility
- DEase of ignition
10.Which of the following properties decreases as the chain length of a hydrocarbon increases?
Medium
- AFlammability
- BViscosity
- CBoiling point
- DMelting point
11.Which of the following statements about cracking are correct? (select all that apply)
Medium
- ACracking converts long-chain hydrocarbons into shorter-chain molecules.
- BCracking produces only alkanes.
- CCracking can be carried out using a catalyst or steam.
- DCracking is a chemical change.
- ECracking is used to increase the supply of short-chain fuels such as petrol.
12.Match each fraction of crude oil to its main use.
Medium
- Liquefied petroleum gas
- Petrol
- Kerosene
- Diesel oil
- Bitumen
- Domestic heating and cooking
- Fuel for cars
- Jet fuel
- Fuel for diesel engines
- Making roads
13.Arrange the following fractions in order of increasing boiling point (lowest first).
Medium
- Liquefied petroleum gas
- Petrol
- Kerosene
- Diesel oil
- Bitumen
14.Which of the following is the correct balanced equation for the complete combustion of methane?
Hard
- ACH4 + 2O2 → CO2 + 2H2O
- BCH4 + O2 → CO2 + H2O
- CCH4 + 3O2 → CO2 + 2H2O
- DCH4 + 2O2 → CO + 2H2O
15.Alkenes are more reactive than alkanes because they contain a carbon–carbon double bond.
Medium
True or false?
16.What is the colour change when bromine water is added to an alkene?
Medium
- AOrange to colourless
- BColourless to orange
- CBlue to colourless
- DYellow to orange
17.Which product is formed during the incomplete combustion of a hydrocarbon fuel such as propane?
Easy
- Asulfur dioxide
- Boxygen
- Chydrogen
- Dcarbon monoxide
18.Which of the following is the formula of a hydrocarbon?
Easy
- AC6H5OH
- BCH2OHCH2OH
- CH2C=CHCH2CH3
- DC6H12Cl2
19.Which molecule can be cracked to produce hexane, C6H14?
Medium
- AC4H8
- BC4H10
- CC6H12
- DC10H22
20.Which of these mixtures shows formulae of substances that could be in the gaseous fraction of crude oil?
Medium
- AC2H4, C3H8, C4H10O
- BC2H4, C3H7Br, C4H10
- CC2H6, C3H8, C4H10
- DC2H6, C3H7Br, C4H10O
21.Sulfur dioxide is formed when energy is released from burning a fuel. Which reaction releases energy from a fuel?
Medium
- ARespiration
- BCombustion
- CNeutralisation
- DDecomposition
22.Decane, C10H22, can be cracked to produce one molecule of ethene, C2H4, and one molecule of CxH18. Determine the value of x.
Hard
- A6
- B7
- C8
- D10
23.Which of the following statements about the products of cracking are correct? (select all that apply)
Medium
- ACracking produces alkenes.
- BCracking produces only alkanes.
- CCracking produces hydrogen.
- DCracking produces carbon dioxide.
- ECracking produces smaller molecules than the starting hydrocarbon.
24.Which of the following statements about the bromine water test are correct? (select all that apply)
Medium
- ABromine water is an orange solution.
- BAn alkane decolourises bromine water.
- CAn alkene decolourises bromine water.
- DThe test relies on the presence of a C=C double bond.
- EAn alkane turns bromine water colourless.
25.Which of the following statements about the combustion of hydrocarbons are correct? (select all that apply)
Medium
- AComplete combustion produces carbon dioxide and water.
- BIncomplete combustion produces carbon monoxide.
- CComplete combustion occurs when oxygen is limited.
- DIncomplete combustion produces soot (carbon).
- EComplete combustion produces carbon monoxide.
26.Crude oil is a finite resource.
Easy
True or false?
27.Fractional distillation of crude oil involves chemical reactions that break down hydrocarbons.
Easy
True or false?
28.As the chain length of a hydrocarbon increases, its boiling point increases.
Easy
True or false?
29.Alkenes are saturated hydrocarbons.
Medium
True or false?
30.Match each combustion product to the environmental issue it causes.
Medium
- Carbon dioxide
- Carbon monoxide
- Sulfur dioxide
- Oxides of nitrogen
- Global warming
- Toxic gas
- Acid rain
- Acid rain and photochemical smog
31.Arrange the following fractions of crude oil in order of increasing boiling point (lowest first).
Medium
- Liquefied petroleum gas
- Petrol
- Kerosene
- Diesel oil
- Heavy fuel oil
- Bitumen
32.A student writes the formula for an alkane as C5H10. Which statement explains why this formula is wrong?
Medium
- AAlkanes have the general formula CnH2n+2, so C5H10 would be an alkene
- BAlkanes have the general formula CnH2n, so C5H10 is correct
- CAlkanes contain oxygen, so the formula should be C5H10O
- DAlkanes have the general formula CnH2n-2, so C5H10 has too many hydrogens
33.A fractionating column has a temperature gradient from 400°C at the bottom to 40°C at the top. A hydrocarbon mixture containing molecules with boiling points of 50°C, 120°C, 250°C and 350°C is fed into the column. Which boiling point corresponds to the fraction collected at the very top of the column?
Medium
- A50°C
- B120°C
- C250°C
- D350°C
34.A hydrocarbon with the formula C12H26 is cracked. Which of the following could be the products of this cracking reaction? (select all that apply)
Hard
- AC8H18 and C4H8
- BC6H14 and C6H12
- CC10H22 and C2H6
- DC5H12 and C7H14
- EC4H10 and C8H18
35.When bromine water is added to an alkene, the orange colour disappears because the bromine atoms add across the carbon–carbon double bond.
Easy
True or false?
36.A student investigates four hydrocarbon fuels by burning them and measuring the mass of soot produced per gram of fuel burned. The results are: Fuel A: 0.02 g, Fuel B: 0.15 g, Fuel C: 0.08 g, Fuel D: 0.25 g. Which fuel is most likely to have the longest hydrocarbon chains?
Medium
- AFuel D, because longer chains burn less cleanly and produce more soot
- BFuel A, because shorter chains burn less cleanly and produce more soot
- CFuel B, because medium chains produce the most soot
- DFuel C, because it produces an intermediate amount of soot
37.Match each crude oil fraction to its main use.
Medium
- Liquefied petroleum gas
- Kerosene
- Bitumen
- Domestic heating and cooking
- Jet fuel
- Making roads
38.A cracking reaction produces ethene, C2H4, and another hydrocarbon. The reactant is an alkane with 14 carbon atoms. What is the molecular formula of the other product?
Medium
- AC12H26
- BC12H24
- CC12H28
- DC14H30
39.A fuel oil fraction contains a mixture of hydrocarbons. Which statements about the properties of this fraction are correct? (select all that apply)
Hard
- AIt has a higher viscosity than petrol.
- BIt is more flammable than petrol.
- CIt has a higher boiling point than petrol.
- DIt is less easily ignited than petrol.
- EIt has a lower boiling point than petrol.
40.In the industrial cracking of long-chain hydrocarbons, what is the catalyst used?
Easy
- AAluminium oxide
- BIron
- CNickel
- DPlatinum
41.Name the homologous series that has the general formula CnH2n+2.
Easy
42.Name the process used to break long-chain hydrocarbons into shorter, more useful molecules.
Medium
43.Complete the sentences about the products of combustion.
Medium
Complete combustion of a hydrocarbon produces carbon dioxide and ____. Incomplete combustion can produce carbon monoxide and ____.
44.A hydrocarbon has the formula C8H18. How many hydrogen atoms are in one molecule?
Medium
45.Complete the sentences about the formation of acid rain.
Medium
Sulfur dioxide dissolves in rainwater to form ____ acid. Nitrogen dioxide dissolves in rainwater to form nitric acid and ____ acid.
46.Decane, C10H22, is cracked to produce one molecule of ethene, C2H4, and one molecule of CxH18. What is the value of x?
Hard
47.Complete the sentences about the two types of combustion.
Easy
In ____ combustion, there is a plentiful supply of oxygen and the products are carbon dioxide and water. In ____ combustion, there is a limited supply of oxygen and the products include carbon monoxide and carbon (soot).
48.A sample of crude oil contains 25% diesel oil by mass. Calculate the mass of diesel oil in a 200 kg barrel of this crude oil. Give your answer in kg.
Medium
49.Complete the sentences about the products of the complete combustion of a hydrocarbon fuel.
Medium
Complete combustion of a hydrocarbon produces carbon ____ and water. The carbon and hydrogen in the fuel are ____ during the reaction.
50.A barrel of crude oil from a well contains 15% kerosene by mass. The barrel weighs 130 kg. Calculate the mass of kerosene in the barrel, in kg.
Easy
51.Complete the sentences about the two types of combustion of a hydrocarbon fuel.
Medium
In complete combustion, there is an excess supply of oxygen, and the products are carbon dioxide and ____. In incomplete combustion, there is a limited supply of oxygen, and the products include carbon monoxide, carbon and ____.
52.Name the homologous series that has the general formula CnH2n.
Easy
53.Explain how fractional distillation separates crude oil into fractions.
Hard
54.Describe how you would test a gas to see if it is an alkene, and state the result.
Hard
55.A student bubbles a gaseous product from cracking through bromine water and observes that the orange colour disappears. Explain what this result tells you about the product and why it occurs.
Hard
56.Describe how you would test an unknown gas to see if it is an alkene, and state the result you would expect.
Hard
57.Explain why cracking is necessary in the oil industry.
Hard
58.A hydrocarbon has the formula C8H18. How many hydrogen atoms are in one molecule?
Medium
- A20 atoms
- B17 atoms
- C18 atoms
- D19 atoms
59.Decane, C10H22, is cracked to produce one molecule of ethene, C2H4, and one molecule of CxH18. What is the value of x?
Hard
- A7
- B8
- C9
- D10
60.A sample of crude oil contains 25% diesel oil by mass. Calculate the mass of diesel oil in a 200 kg barrel of this crude oil. Give your answer in kg.
Medium
- A50 kg
- B45 kg
- C60 kg
- D55 kg
61.A barrel of crude oil from a well contains 15% kerosene by mass. The barrel weighs 130 kg. Calculate the mass of kerosene in the barrel, in kg.
Easy
- A18.5 kg
- B19.5 kg
- C20.5 kg
- D21.5 kg

Kartu flash

What is a hydrocarbon?

A compound that contains hydrogen and carbon atoms only.

What is crude oil?

A complex mixture of lots of different hydrocarbon compounds of different sizes. It is a thick, sticky, black liquid found in porous rock.

Why is crude oil described as a finite resource?

It formed over millions of years from the remains of plants and animals, mainly plankton, buried in mud, and is being used up much faster than it is being formed.

What is the general formula of the alkanes?

CnH2n+2

Name the first four members of the alkane homologous series.

Methane, ethane, propane and butane.

What does 'saturated' mean when describing a hydrocarbon?

It contains only single carbon-carbon bonds, with no double bonds.

What is a homologous series?

A family of organic compounds with the same functional group, the same general formula and similar chemical properties, in which each member differs from the next by CH2.

What is fractional distillation used for?

To separate crude oil into fractions, each containing hydrocarbons of similar chain length, according to their boiling points.

Explain how fractional distillation separates crude oil.

Crude oil is heated and vaporised; vapours rise up a column with a temperature gradient. Hydrocarbons with high boiling points condense low down, and those with low boiling points rise and condense near the top.

How do boiling point, viscosity and flammability change as hydrocarbon molecules get larger?

Boiling point increases, viscosity increases and flammability decreases.

Why do larger hydrocarbon molecules have higher boiling points?

The intermolecular forces of attraction between the molecules are greater, so more energy is needed to separate them.

Give two uses of fractions obtained from crude oil.

Petrol is used as fuel for cars and kerosene is used as jet fuel (also: diesel for diesel engines, heavy fuel oil for ships and power stations, and liquefied petroleum gas for domestic heating and cooking).

What is complete combustion of a hydrocarbon?

Burning with an excess supply of oxygen, producing carbon dioxide and water.

What is incomplete combustion of a hydrocarbon?

Burning with an insufficient supply of oxygen, producing carbon monoxide, carbon (soot) and water.

Why is carbon monoxide dangerous?

It is a toxic, odourless gas that binds to haemoglobin, preventing it from carrying oxygen, which can cause dizziness, loss of consciousness and eventually death.

Write the word equation for the complete combustion of propane.

Propane + oxygen → carbon dioxide + water

How is sulfur dioxide formed when fuels burn, and why is it a problem?

Fossil fuels often contain sulfur impurities, which are oxidised to sulfur dioxide during combustion. It dissolves in rainwater to form acid rain, which corrodes buildings and damages aquatic organisms.

How are oxides of nitrogen formed in a car engine?

Nitrogen and oxygen from the air react at the high temperatures and pressures inside the engine, forming nitrogen monoxide and nitrogen dioxide.

What is the job of a catalytic converter?

It uses transition metal catalysts such as platinum, palladium and rhodium to convert pollutant gases into less harmful ones, oxidising carbon monoxide and unburnt hydrocarbons and reducing nitrogen oxides to nitrogen.

What is cracking?

An industrial process that breaks low-demand, long-chain hydrocarbon molecules into more useful, shorter-chain molecules, producing alkanes and alkenes.

Give the conditions used for catalytic cracking.

The hydrocarbons are heated to about 470–550°C to vaporise them, then the vapours pass over a hot powdered aluminium oxide catalyst.

Why is cracking economically necessary?

The demand for short-chain fractions such as petrol, kerosene and diesel is greater than the supply, while long-chain fractions such as fuel oil are in surplus, so cracking converts the unwanted fractions into more useful ones.

What is the general formula of the alkenes?

CnH2n

What is the difference between alkanes and alkenes?

Alkanes are saturated, containing only single carbon-carbon bonds, while alkenes are unsaturated, containing at least one carbon=carbon double bond.

Describe the test used to distinguish an alkane from an alkene.

Add bromine water: with an alkene the orange colour decolourises, but with an alkane it stays orange.

State one advantage and one disadvantage of using hydrogen as a fuel.

Advantage: it releases more energy per kilogram than any other fuel and only produces water when it burns, so it does not pollute. Disadvantage: it is expensive to produce, requires energy to make, and is difficult and dangerous to store and transport.

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